Tailoring flow behavior and texture of water continuous cocoa suspensions

The microstructure of low fat food suspensions must be carefully adjusted to meet customer expectance. Here we discuss how appropriate heat treatment or the addition of an adequate immiscible secondary fluid can be used to tailor the texture and flow of water based cocoa suspensions in a wide range. Comparing suspensions of untreated and organic solvent (n-hexane and ethanol) extracted cocoa particles we demonstrate that the residual cocoa butter is decisive for the control of the structure and flow behavior of these suspensions. Upon heating to 30-35 °C the low shear viscosity and apparent yield stress of suspensions from untreated particles increases by more than two orders of magnitude and this is attributed to the formation of a particle network hold together by the sticky, semi-crystalline cocoa butter leaking from the interior of the particles. This structure remains stable upon cooling to 20°C but it vanishes when the suspension is heated to temperatures T > 40°C. Then the cocoa butter detaches from the cocoa particles forming separate emulsion droplets as confirmed by fluorescence microscopy. A similar structure build-up can be achieved at room temperature if trace amounts of polar organic solvents like oleic acid, octanoic acid or octyl acetate are added. This is attributed to the partial solubility of cocoa butter in these solvents and the formation of a sticky surface layer formed by these butter/solvent mixtures as confirmed by small angle neutron scattering experiments. The solubility rate determines the kinetics of particle network formation. The creamy texture provided by the formation of a particle network either using heat treatment or addition of a secondary fluid opens up new pathways for the formulation of low fat food products based on suspensions of cocoa or other finely dispersed particles.status: publishe